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Lugon-et-l'Île-du-Carnay, France

Stott P.A.,UK Met Office | Christidis N.,UK Met Office | Otto F.E.L.,University of Oxford | Sun Y.,National Climate Center | And 7 more authors.
Wiley Interdisciplinary Reviews: Climate Change

Extreme weather and climate-related events occur in a particular place, by definition, infrequently. It is therefore challenging to detect systematic changes in their occurrence given the relative shortness of observational records. However, there is a clear interest from outside the climate science community in the extent to which recent damaging extreme events can be linked to human-induced climate change or natural climate variability. Event attribution studies seek to determine to what extent anthropogenic climate change has altered the probability or magnitude of particular events. They have shown clear evidence for human influence having increased the probability of many extremely warm seasonal temperatures and reduced the probability of extremely cold seasonal temperatures in many parts of the world. The evidence for human influence on the probability of extreme precipitation events, droughts, and storms is more mixed. Although the science of event attribution has developed rapidly in recent years, geographical coverage of events remains patchy and based on the interests and capabilities of individual research groups. The development of operational event attribution would allow a more timely and methodical production of attribution assessments than currently obtained on an ad hoc basis. For event attribution assessments to be most useful, remaining scientific uncertainties need to be robustly assessed and the results clearly communicated. This requires the continuing development of methodologies to assess the reliability of event attribution results and further work to understand the potential utility of event attribution for stakeholder groups and decision makers. © 2016 Wiley Periodicals, Inc. Source

Kinney P.L.,Columbia University | Schwartz J.,Harvard University | Pascal M.,Institute of Veille Sanitaire | Petkova E.,National United University | And 3 more authors.
Environmental Research Letters

Extreme heat events are associated with spikes in mortality, yet death rates are on average highest during the coldest months of the year. Under the assumption that most winter excess mortality is due to cold temperature, many previous studies have concluded that winter mortality will substantially decline in a warming climate. We analyzed whether and to what extent cold temperatures are associated with excess winter mortality across multiple cities and over multiple years within individual cities, using daily temperature and mortality data from 36 US cities (1985-2006) and 3 French cities (1971-2007). Comparing across cities, we found that excess winter mortality did not depend on seasonal temperature range, and was no lower in warmer vs. colder cities, suggesting that temperature is not a key driver of winter excess mortality. Using regression models within monthly strata, we found that variability in daily mortality within cities was not strongly influenced by winter temperature. Finally we found that inadequate control for seasonality in analyses of the effects of cold temperatures led to spuriously large assumed cold effects, and erroneous attribution of winter mortality to cold temperatures. Our findings suggest that reductions in cold-related mortality under warming climate may be much smaller than some have assumed. This should be of interest to researchers and policy makers concerned with projecting future health effects of climate change and developing relevant adaptation strategies. © 2015 IOP Publishing Ltd. Source

Telford P.J.,University of Cambridge | Lathiere J.,University of Sheffield | Lathiere J.,Lancaster University | Lathiere J.,Laboratoire Des Science Du Climat Et Of Lenvironment | And 14 more authors.
Atmospheric Chemistry and Physics

In the 1990s the rates of increase of greenhouse gas concentrations, most notably of methane, were observed to change, for reasons that have yet to be fully determined. This period included the eruption of Mt. Pinatubo and an El Niño warm event, both of which affect biogeochemical processes, by changes in temperature, precipitation and radiation. We examine the impact of these changes in climate on global isoprene emissions and the effect these climate dependent emissions have on the hydroxy radical, OH, the dominant sink for methane. We model a reduction of isoprene emissions in the early 1990s, with a maximum decrease of 40 Tg(C)/yr in late 1992 and early 1993, a change of 9%. This reduction is caused by the cooler, drier conditions following the eruption of Mt. Pinatubo. Isoprene emissions are reduced both directly, by changes in temperature and a soil moisture dependent suppression factor, and indirectly, through reductions in the total biomass. The reduction in isoprene emissions causes increases of tropospheric OH which lead to an increased sink for methane of up to 5 Tg(CH4)/year, comparable to estimated source changes over the time period studied. There remain many uncertainties in the emission and oxidation of isoprene which may affect the exact size of this effect, but its magnitude is large enough that it should remain important. © 2010 Author(s). Source

Saurer M.,Paul Scherrer Institute | Spahni R.,University of Bern | Frank D.C.,Swiss Federal Institute of forest | Frank D.C.,University of Bern | And 31 more authors.
Global Change Biology

The increasing carbon dioxide (CO2) concentration in the atmosphere in combination with climatic changes throughout the last century are likely to have had a profound effect on the physiology of trees: altering the carbon and water fluxes passing through the stomatal pores. However, the magnitude and spatial patterns of such changes in natural forests remain highly uncertain. Here, stable carbon isotope ratios from a network of 35 tree-ring sites located across Europe are investigated to determine the intrinsic water-use efficiency (iWUE), the ratio of photosynthesis to stomatal conductance from 1901 to 2000. The results were compared with simulations of a dynamic vegetation model (LPX-Bern 1.0) that integrates numerous ecosystem and land-atmosphere exchange processes in a theoretical framework. The spatial pattern of tree-ring derived iWUE of the investigated coniferous and deciduous species and the model results agreed significantly with a clear south-to-north gradient, as well as a general increase in iWUE over the 20th century. The magnitude of the iWUE increase was not spatially uniform, with the strongest increase observed and modelled for temperate forests in Central Europe, a region where summer soil-water availability decreased over the last century. We were able to demonstrate that the combined effects of increasing CO2 and climate change leading to soil drying have resulted in an accelerated increase in iWUE. These findings will help to reduce uncertainties in the land surface schemes of global climate models, where vegetation-climate feedbacks are currently still poorly constrained by observational data. © 2014 John Wiley & Sons Ltd. Source

Poberaj C.S.,ETH Zurich | Staehelin J.,ETH Zurich | Bintania R.,Royal Netherlands Meteorological Institute | Van Velthoven P.,Royal Netherlands Meteorological Institute | And 9 more authors.
DLR Deutsches Zentrum fur Luft- und Raumfahrt e.V. - Forschungsberichte

In the EU Integrated project QUANTIFY, atmospheric chemistry models (ACMs) are one of the major tools to improve the understanding of key processes relevant for the effects of different transportation modes, and their representation in global models. The performance of the ACMs has been tested through comparisons with the ETH model evaluation global database for the upper troposphere and lower stratosphere. Data from measurement campaigns, ozone soundings, and surface data have been processed to support an easy and direct comparison with model output. Since model evaluation focuses on the year 2003, observational data to compare model data with are the SPURT campaign and the commercial aircraft program MOZAIC. The model evaluation indicates a particular problem in the simulation of carbon monoxide. If QUANTIFY emissions inventories are used, models significantly underestimate its tropospheric abundance at northern hemispheric middle latitudes and subtropical latitudes. Potential causes will be discussed. Source

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